A Spatial light modulator (SLM) is one of an array of optical elements (pixels) in which each pixel acts independently as an optical “valve” to adjust or modulate light intensity. The modulation of pixels is accomplished electronically based on image data, essentially converting image information from the electronic domain into light. An SLM does not create its own light, but rather modulates (either reflectively or transmissively) light from a lamp or laser source to create a dynamically reconfigurable digital image.
SLMs are used in many technical areas in order to control light on a pixel-by-pixel basis, such as optical data processing, adaptive optics, optical correlation, machine vision, image processing and analysis, beam steering, holographic data storage, displays and MEMS devices (e.g., digital micromirror device (DMD) or the grating light valve (GLV) device). The most typical applications of SLMs are for digital displays, consumer TVs, and office projectors.
The basic structure of an SLM includes a reflecting surface, a hinge member, and one or more electrodes. One electrode can be charged with a voltage while the reflecting surface is oppositely charged causing an electrostatic attraction between the underside of the reflecting surface and the electrode. This electrostatic attraction is enough to deform the hinge, upon which the reflecting surface sits, and to tilt the reflecting surface in the desired direction.
To return the reflecting surface to its original position, the electrode and the reflecting surface are driven to the same voltage level (e.g., ground) releasing the electrostatic attraction. The hinge member acts as a spring and returns to its natural, at-rest position, much like a bent tree limb springs back to its natural position.
A cross-sectional view of a SLM 100 is shown in FIG. 1. The SLM includes a base 102 and two opposing electrodes, shown generally at 106, 108. Opposing spring fingers 110, 112 are mounted above the electrodes and generally stop the rotation of a reflecting surface 114 as it rotates towards one of the electrodes 106, 108. The reflecting surface 114 rotates by means of a hinge, shown generally at 116. The hinge is a solid, elongated piece (not shown) having the ability to deform under force and return to its natural position once the force is removed. FIG. 1 shows a spatial light modulator in the activated or “ON” position. To activate the spatial light modulator, the electrode 106 is positively charged, while the underside of the reflecting surface 114 is negatively charged causing the reflecting surface to rotate about hinge 116 until the reflecting surface contacts spring finger 110. In this position, deflected light 122 has an angle of reflection desirable to project the light beam 118 from a light source 120 towards, for example, a pixel 124 on a display,
FIG. 2 shows the same spatial light modulator 100 in a deactivated or “OFF” position. In this view, the reflecting surface 114 is rotated toward the opposing electrode 108 until the reflecting surface 114 contacts spring finger 112. In this position, the directional light 118 is deflected into a light absorber 126.
Current designs of the hinge member are not ideal for the proper operation of the SLM. For example, the SLM may required a high actuation voltage in order to deform the hinge. Likewise, the hinge member may have a slow spring-back time to return to its natural position hindering the speed of the SLM. The hinges are also vulnerable to hinge thickness variations during the manufacturing process that can cause non-uniform rotation. The thickness variations also affect the ability to further reduce the size of the hinge, which ultimately limits its speed.
Thus, it is desirable to increase the speed and efficiency of an SLM.